I would continue to try to work through the dilators focusing on getting them through the first set of muscles. It is possible, that as you continue to dilate and move bigger, you will also be slowly learning to relax the deeper muscles as well.
You won’t do any damage inserting a dilator “too far” if you are going slow. The dilator can press up against the cervix without any harm, it might not feel great, but would be ok.
I would also consider trying to find a dilator that is the same width as the smallest one you have no pain with, but longer. Maybe if you use a very small dilator, but can insert it further, that will also help.
You might also really benefit from intravaginal valium suppositories to help with the deeper muscle spasm.